Snap acting control device



Feb. 12, 1946.

IJ. R. CAMPBELL 1 t e e .n S s t e e h S 5 E C I m@ D9 L1 m 5 Ml ou Cn Ga NJ Md om. Ai PF A N s rfi-M55 j?, CP1/14,055, INVENTOR.

ATTORNEY.

Ill/Il Feb. 12, 1946. J. R. CAMPBELL SNAP ACTING CONTROLy DEVICE Filed Jan. ll5, 1945 5 .Sheets-Sheet 2 INVENTOR.

ATTORNEY.

Feb. 12, 1946. i L R, CAMPBELL 2,394,747

SNAP ACTING CONTROL DEVICE Filed Jan. 15, 1945 5 Sheets-Sheet 3 4,145.5 Je. C21/14,0551. L,

IN V E NTOR.

MMM/,7V

ATTORNEY.

Feb. 12, 1946. .1. R. CAMPBELL 2,394,747

simD ACTING N'rRoL DEVICE Filed Jan. 15,1945 5 sheets-sheet 4 U21/w55 Je CAMpa-L .K

1N VEN TOR.

Feb. 12, 1946. 1 R, CAMPBELL 2,394,747

SNAP ACTING CONTROL DEVICE Filed Jan. 15, 1945 5 Sheets-Sheet 5 INVENTOR.

ATTORNEY.

Patented Feb. 12, 1946 2,394,147 SNAP ACTING coNraoL DEVICE James a. campbell,

signor to Paul Henry, Application `lanuary 15, 1945, Serial No. 572,823`

(Cl. 20o-67) 17 Claims.

This invention is concerned with snap acting control mechanisms and aims to provide irnprovements therein. More particularly, the invention has for its object a novel snap action device for the control of valves, switches, and

similar flow interrupting or flow altering 'means as a function of some mechanically registerable change in condition such as temperature, pressure, humidity, or mechanical displacement.

Snap acting devices for -control of flow interrupting or flow altering means, such as valves, switches, and the like, should be positive in action, compact, rugged, and simple in construction; have a minimum of inertia in moving parts, have a minimum of friction in moving parts, be capable of operating on a very small differential of change in the condition to which it is responsive, be substantially unaffected by vibrations and shock, and be applicable and adjustable over a wide range of such condition.

The principal object of my invention is to provide a novel and advantageous type of snap acting control device which will fulfill all of these requirements.

A particular object of this invention is to provide a snap acting control device that will operate positively to actuate a flow controlling or flow interrupting member between its two positions. with a small differential in it is responsive, that is, with a small difference between the values of such condition required for operation to one position or the other.

A further object is to provide a device that' to provide snap ol the can be readily adjusted so as action at different values or magnitudes condition to which it is responsive.

A further object' is to provide a device that is inherently resistant to inadvertent operation from one position to the other due to effects of vibration. In this connection, a particular object is to provide a device utilizing a control member mounted for rotation between its two positions by thrust members responsive to changes in a condition, in which the thrust members are so arranged that the combined effect thereof tending to cause rotation of the control member is substantially unaffected by vibration, and in which the control member is rotationally balanced about its axis of rotation so as to be itself substantially unaffected by vibration.

The device of my invention, by which these desired objectives are accomplished. comprises a central shaft which is resiliently and rotatably engaged and supported by three or more resilient thrust members disposed at different angular pothe condition to which 'build and calibrate but Laguna Beach. Calif., as-

Los Angeles, Calif.

sitions about the central shaft and spaced less than apart, with one or more of said thrustI members affected by a change in condition in a manner to alter its resultant thrust against the central shaft. Rotation of the central shaft is limited by suitable fixed or adjustable stops and in the stop umits when a suitable change in the resultant thrust against the central shaft is efthe thrust members, or vice versa, to various desired positions results in selecting various points or values of the changing condition, at which snap action will occur.

Further, by using three or more angularly spaced thrust members resiliently engaging and supporting the central shaft, the device has the novel feature of being self-aligning and self-com pensating for discrepancies in either the thrust members or the central shaft. By using three equally spaced thrust members, `the resultant forces are always equalized on all members (without adjustment or special operation) in a man-A ner to produce a clearly defined net resultant force which produces the snap action. Also, this construction not only provides an easy device to a'device inherently resistant to effects of vibration. The worst effects of vibration occur when the vibration is imposed in the plane of motion of the moving parts, which in this case would be in a plane through the angularly spaced thrust members and perpendicular to the axis of the central shaft. Under this condition the net effective resultant force on the central shaft remains substantiallyl the same with vibrationbecause one thrust members gain or loss of resultant thrust is the others loss or gain. Also, the rotational snap action of the central shaft allows the use of a rotationally balanced arrangement of the flow interruptvery low moment of inertia. Further. the small diameter of the central shaft member allows positive snap action rotation thereof with small changes in the resultant force of one ormore of the thrust members and hence results in a device with an inherently low operating differential. Because of the aforementioned equalizing action of the three or more thrust members there is no tendency toward instability of operation even on a very small operating differential. 'I'he use of such angiilarly spaced thrust members engaglng a relatively small central shaft offers an ideal means for proper distribution of stresses in the thrust members in that the tendency of a thrust member to exert a rotative thrust on the central shaft can be distributed in a positive and negative sense such that over part of the adjustable range the component of the thrust of such member will be clockwise and over the balance of the adjustable range the tangential component of the thrust will be counterclockwise. This condition provides an adjustable range of approximately twice the magnitude that is possible when a stressed member has all the loading incurred by adjustment taken in one direction only.

In a preferred form of the device, adapted for control of temperature, resilient bimetallic strips having different ratesv of thermal expansion of the two sides are employed for the angularly spaced thrust members. The bimetallic strips are preferably each formed into a series of loops extending substantially equally on both sides of a center line through the'outer or mounting end and the inner or actuating end which engages the central shaft. These resilient bimetallic strips engage the central shaft, preferably through knife edges on the strips and V grooves on the shaft, with an inwardly directed force and it is preferable that the number of loops into which the strip is formed be the same on both sides of the center line so that the amount of inwardly directed force will not changewith temperature changes and the snapping action of the device depends on the change in the tangential component of thrust developed bythe bimetallic strips reaction to temperature changes.

My invention will be more thoroughly understood in the light of the following detailed description and accompanying drawings in which:

Fig. i is a side elevation of a form of control device in accordance `With my invention, adapted to open and close switch means in an electric circuit in response to variations in temperature;

Fig. 2 is a front elevation thereof, looking in the direction indicated by the arrow 2 in Fig. 1;

Fig. 3 is a vertical section on line 3-3 in Fig. 1;

Fig. 4 is an inverted horizontal section on line 4-4 in Fig. 3;

Fig. 5 is a sectional view on line 5 5 in Fig. 4;

Fig. 6 is a vertical section on line 6--6 in Fig. 1;

Fig. 7 is an enlarged diagrammatic view illustrating the principle of operation of a, control device of the type shown in Figs. 1 to 6;

Fig. 8 is a perspective view of the central shaft and the control member actuated thereby, showing a somewhat modified construction that may :'oe used in some cases; i 4

Fig. 9 is a front elevation of a modified form of control device, responsive to variations in pressure to operate an electric switch; I

Fig. 10 is a'front elevation voi' another form of device, responsive to mechanical displacement to operate an electric switch:

Fig. 11 is a partial vertical elevation (corresponding in aspect to a portion of Pig. 3) showing an advantageous form of rotatably mounted switching means and associated contact members;

Fig. 12 is a sectional view on line I2|2 in Fig. 11;

Fig. 13 is a sectional view on line I3-Il in Fig. 12';

Fig. 14 is a partly sectional front elevation of another modification of the invention, adapted vto operate a valve in a fluid passage, in response to variations in temperature; and

Fig. 15 is a sectional view on line I 5| 5 in Fig. 14.

The control device shown in Figs. 1 to 6 and illustrated diagrammatically in Fig. 7 is of the thermostatic switch type. It comprises a central shaft i resilientiy and rotatably engaged and supported by three temperature-responsive resilient thrust members 2a, 2b and 2c disposed in generally radial directions at different angular positions about said shaft and preferably spaced approximately 120 apart. as best shown in Figs. 6 and 7. Each of said thrust members is shown as a looped bimetallic strip having high-expanding ,and low-expanding side portions 3 and l respectively, secured at its outer end to a lug 5 projecting rearwardly from a supporting plate or disc 6. If desired, I may provide the device with more than three, for example, from four to six, such thrust members, preferably equally spaced from one another aboutthe central shaft. For most purposes, however, I prefer to use only three of these resilient thrust members, as shown.

. Each bimetallic member 2a, 2b and 2c is formed with two loops on each side of the radial center line. A given change in temperature will cause the loops on one side of the center line of each member to open up and those on the other side to close by a substantially equal amount, so that the inwardly directed component of thrust exerted by each of said members against shalt I remains substantially constant despite variations in temperature.

Each of the bimetallic members is preferably bevelled at its inner end to form a knife edge (as shown more clearly at l in Fig. 7), which engages shaft I in a V-shaped groove or indentation 8, said shaft being provided with three such grooves extending longitudinally and spaced approximately 120 apart circumferentially, to receive the knife-edged inner ends of the corresponding bimetallic thrust members. Each of the V-shaped notches or grooves is preferably rounded somewhat at its inner end, on a small radius of curvature, so as to ensure smooth' rolling contact of the knife-edge tip l with the surface thereof and thus provide smooth and positivev operation. The angle of each V-shaped groove l is shown as approximately while the angle of knife-edge 1 is shown as about 20, thus permitting angular adjustment of the thrust members relative to the shaft as described hereinafter.

' Connected" to the forwardend of shaft I is a control member comprising bar II extending diametrically with respect to said shaft and 'formed of mica. or other suitable insulating material. Said'control member functions as a switch for opening and closing an electric circuit, and also serves to limit the snap action rotative movement of the shaft in each direction by engagement with suitably positioned stop means.

Contact members I2a and |212y are mounted on the respective ends of bar II and are connected together by a conducting strip I3 whose central portion is brackets Ita and Bald pin extends through wise direction in Fig.

lli'ig. 8, in which bar II bowed outwardly so as to be spaced from and free from contact with the means connesting the bar to shaft I. Fixed contact members Ila and IIb are mounted on supporting Ilb secured to a supporting plate or disc I6 formed of mica or other suitable insulating material, and are positioned for engagement by contact members I2a and I2b upon movement of bar II in a counter-clockwise direction in Fig. 3, thus acting as stop members limiting rotative movement of shaft I in that direction. The forwardly projecting arms I1a and Ilb of brackets Ila and Ib secured to supporting plate I8 are positioned for engagement by the respective ends of bar II, and act as stop means to'limit rotative movement of said bar and shaft I in the reverse direction. Shaft I extends through a sleeve Il which engages centrally located openings in plates 8 and I8 and connects these plates together. while permitting relative rotation thereof for adjustment purposes as described hereinafter.

The switch shown is of the single throw type, adapted to close connection between contacts Ila and IIb on movement in one direction and to open the circuit upon movement in the opposite direction., It will be obvious that, if a double throw type of switch is desired, bar Il could be provided with an additional set of contact members adapted to engage contact members secured to stop members Ila and I1b upon clockwise rotation in Fig. 3, in order to close another circuit.

In order to ensure good contact between contacts I2a, I2b and Ila, IIb, the bar II preferably mounted on shaft I in such manner as to permit'pivotal movement thereof about an axis extending parallel to the length of said bar. Thus, bar II is shown as securedby a. rivet 2I to a forwardly projecting lug 22 on a metal strip 2I'whose outer ends are bent rearward as shown at 24 and rotatably engage a pin 25.

the forward end of shaft I, parallel to bar II. Pin 2B may be rotatably, mounted in shaft I or rigidly secured thereto, but is heid against longitudinal movement relative to said shaft and also relative to strip 28: Upon rotation of shaft I in a counter-clock- 3, bar II is free to rock about the axis of pin 2l to a position in which contacts I2a and I2b firmly engage fixed contacts Ila and IIb, respectively..

For some purposes. the control member actuated by the shaft may be rigidly secured thereto. Buch a construction is illustrated in of rivet 28. Shaft I' the shaft I', as by means Ais connected rigidlyy to is provided with V-shaped grooves Il for supporting engagement by resilient thrust members, and bar I I' is adapted to engage stop means upon movement in either direction and is provided with contact members I2a and I2b and conductor strip Il. in the same manner as described above.

Suitable means are provided for maintaining the thrust member supporting plate 6 and the stop meanssupporting plate I8 in the desired relative positions, and preferably for enclosing the above described mechanism. I also prefer to provide for adjustment of the angular position of the radially disposed thrust members with respect 'to shaft I, in order to vary the temperature at which the device may be set to operste. Due to engagement of bar II with stop members Ila, I2b or Ila, I1b, the limits of angular movement of the shaft I are defined by the relation. whereby the and I have therefore 'plate i, it is position of plate Il. while -the angular position of thrust members 2a. 2b and 2c is defined by the position of plate l. Thus, the adjustment to cause the snap action to occur at'different temperature values may rotation of plates I and Il about shaft I. Either or 'both of these plates might be rotatably mounted for this purpose. However, it is generally desirable to avoid moving the contact members Ila and Hb in effecting this adjustment, shown a construction in which plate I8 is held in fixed position within a suitable housing while plate t is rotatably mounted.

Thus, the mechanism is shown as enclosed within a metal housing comprising front and rear casing members 2I and 32. The front casing member 3l is provided with a central forwardly extended portion 2l to receive the control bar II and the associated contact means and stop members, and the rear end thereof is flanged outward at u. The rear casing member 32 is provided with an enlarged portion 25 to receive the peripheral portions of plates 6 and I6 between flange 24 and a corresponding flange 38 on said casing member, plate 6 having its peripheral portion offset forwardly as shown. at Ii'.

A spacer ring 21 is interposed between said flanges to maintain sufllcient space therebetween to permit rotation of plate 8. The forward end of casing member I2 is bent inward over flange 3l, as shown at 38, to secure the casing members together. When the parts are thus secured,

the peripheral portion 8' of `plate 6 is in frictional engagement with plate I8 and casing mem ber I2, and may if desired be provided with a roughened surface or with slight indentations at its position of engagement with the casing, for the purpose of holding it in position during initial adjustment and until it is secured in properly adjusted position as described hereinafter.

When the device is intended for operation in response to variations in temperature of al1-'or other gas, the' rear casing member 22 is preferably provided with one or more openings 4I to permit access of gas to the .bimetallic elements 2a, 2b and 2c.

In order to provide provided with a projection 42 extending through an arcuate slot of suitable extent, say about in the housing, members 35 and 21 being eut away as indicated at I5 and 21' to provide said slot. f

The .brackets im, wb and Ita, Itb are secured to insulating plate I8, as by means of rivets I2. Brackets Iba and Ib are provided with forwardly projecting terminal lugs a and b which extend with clearance through openings in the casing and may be provided with threaded openings 4I for attaching lead wires. Segment shaped plates 41 of mica or other suitn able insulating material are provided inside the upper and lower portions of the front casing member SI, and are secured thereto against relative turning movement by means of rivets 48 and by engagement of their arcuate outer edge portions with the cylindrical side wall portion of said casing member. Said insulating plates 41 are provided with openings 49 through which terminal lugs a and b extend in close-fitting engagement of said terminal lugs with said insulating plates serves to prevent rotation of insulating plate I6 and the parts carried thereby. relative to the casing.

The principle of operation of this form of debe eifected by relative for rotative adjustment of vice may best be explained with reference to Fig. 7, which shows the most essential parts somewhat diagrammatically, including shaft l, bime- I Nb, lla and I 1c mounted on supporting plate i6. This view is generally comparable to Fig. 6 although, for simplicity and clarity of illustrationI bar Il is shown rigidly connected to shaft i as in the form shown in Fig. 8, and bar il and the associated stop members are shown in a different angular relation to shaft l and its supporting thrust members, this particular angular relationship being immaterial.

The device is assembled with the resilient thrust members 2a, 2b and 2c under .longitudinal compression, so that each of said members exerts an inward thrust against shaft I, of sufficient magnitude to require the storing of considerable energy due to tangential force created by a temperature change before the shaft is rotated, so that movement of the shaft will always occur by snap action rather than as a gradual creeping movement. At some given temperature, the thrust members will exert no thrust in a tangential direction, so that the force exerted will be simply an inward force due t the longitudinal compression thereof. The inward force so exerted by thrust member 2a is indicated at Fi, which in this position ofA the thrust member passes through the axis of rotation of the shaft, indicated at 0, Since the thrust members are bimetallic elements as described above, member 2a Wili exert a tangential component of force in the direction indicated at Tr upon an increase of temperature, and in the direction indicated at To upon a decrease of temperature.

lf the temperature is increased so as to produce a tangential component of force T1, the resultant force exerted by member 2a is indicated at R1, tending to cause clockwise'rotation of shaft l. The same considerations apply to they other thrust members. When the combined moment of the resultant forces exerted thereby is in a clockwise direction, the control bar is moved to and held in the position indicated, in contact with stop members ilo and Hb. These members are electrical contacts as noted above, and an electrical connection is thus established there-- between.

If the temperature decreases until the combined moment of the resultant forces exerted by the thrust members is in the reverse direction, shaft i will be rotated counterciockwise by snap action, moving bar ii into engagement with stop members ila and ilb. Thus, upon an increase of temperature above, or a decrease of temperature below, the temperature at which the device is set to operate, the control bar will be moved by snap action to either close or open the electrical connection between contact members Ha and Hb. f

Ii it is desired to set the device to operate at a higher temperature, supporting plate 8 and the thrust members carried thereby may be rotated clockwise relative to supporting plate I8,

so as to shift the longitudinal axis of thrust member 2a, for example, to a position such as shown by the dotted line at 2a. In this position, a certain definite tangential component of iorce due to temperature, indicated at Ta, will be required to produce in combination with inward force F2 a resultant Ra passing through the axis of the shaft, so that a higher temperature isrsquired to cause snap action of the shaft in a clockwise direction to bring bar i I into engagement with contact members Ila and IIb, while counterclockwise snap action rotation in the reverse direction also occurs/at a higher temperature. Since the diameter of shaft is quite small as compared to the effective length of each of the thrust members, rotative adjustment of the supporting plate i as above described will not introduce anl appreciable change in the magnitude of the inwardly directed force F. Furthermore, the change in magnitude of the tangential component of force produced by such adjustment is relatively small compared to the changes in such component produced by vchanges in temiperature.

Whenever the resultant R of the inward component of force F and the tangential component T exerted by each thrust member passes through the axis of rotation of the shaft, the thrust member tends to produce rotation of the shaft, and when the combined moment produced by the three thrust members passes through zero the shaft is rotated from engagement with one set of stop members into engagement with the other. The shift in position will always occur with snap action because the initial movement increases the lever arm of each thrust member and thus increases the moment in that direction. causing the control bar to snap to its position against the other set of stop members.

Since, as explained above, rotative adjustment of the thrust members serves to vary the tangential component required to produce a resultant force R passing through the axis 0, it will be evident that plate 6 may be rotated by manipulation of the projection 4 2, to adjust the device for operation at the desired limits of temperature, within the range of temperature limits for which the device is intended. When so adjusted, the plate 6 may be locked in this position, as by soldering, crimping, or otherwise 'securing the projection 6 tightly to the' casing.

The same essential features and principles of operation can be adapted for operation in responses to changes in other conditions than temperature. For operation in response to humidity, the bimetallic elements above described may be replaced by elements that are movable in response to variations in humidity. For example, each of the three resilient thrust members Ia, 2b and 2c may comprise an element of similar shape and relative position to the bimetallic elements, formed of a thin strip of resilient metal bonded to a strip of paper or other material adapted to expand upon absorption of moisture.

A form of snap acting control device responsive to variations in pressure is shown in Fig. 9. The central shaft 5| is rotatably engaged and supported by three angularly spaced Bourdon tubes 52a, 52h and 52o, each of which is resilient and is compressed in a radial direction so as to exert an inward thrust against the shaft. The inner ends ofthe Bourdon tubes are closed by members 53 provided with knife-edge tips engaging V- shaped grooves or indentations I4 in shaft Il. Each Bourdon tube is connected at its outer end to a lug 55 which is integral with ring l0 secured to'an insulating plate I1 by means of releasable clamp members I8, whereby the outer ends of the Bourdon tubes may be rotatably adjusted about the axis of the shaft and secured in the desired relative position. Ring 5I is provided with a nozzle l! for connection to a. source of variable fluid pressure, and said ring-md lugs i said shaft in the same manner as bar rection. When the Il are provided with passages leading from said nozzle to the interiors of the Bourdon tubes.

The Bourdon tubes are of spiral form so that changes in fluid pressure therein will produce changes in thrust substantially perpendicular to the inwardly directed thrust due to radial compression of the tubes. Thus, the directions of thrust due to increase and decrease in pressure are indicated by the arrows at Tr and To respectively.

The control member is again shown as an insulating bar 6| operatively connected to shaft 5| and extending substantially perpendicular thereto, said bar being either pivotally mounted on in Fiss. 3 to 5 or rigidly connected thereto in thesame manner as the bar il' in Fig. 8.

Stop members 62a, B2b, 63a, mounted on supporting plate 51. Members 82a and 62h are positioned to engage the end 4portions of bar 6| upon rotation in a counterclockwise direction, while members 83a and 63h are positioned to engage the end portions of said bar upon rotation in a clockwise direction. thus serving to limit the rotative movement of the shaft.

and 63h are As before, either one or both of the sets of travely limiting stop members may also serve as electrical contacts, but I have again shown only members 8221 and 62h functioning as contacts, insulating bar 6| being provided with coacting contact members by a conductor strip 85.

The plate 51 may be formed of molded plastic material or other suitable insulating material. Said plate may be supported in and ring 56 carrying the Bourdon tubes may be rotated thereon by loosening clamps 58; or ring 58 may be supported in fixed position as by means of nozzle 59, and plate E1 carrying the stop members may be rotated thereon; in either case, such rotative adjustment serves to adjust the angular relation between the pressure-responsive resilient thrust members Mc and the limits of rotative movement of the shaft as dened by stop members 62g, 62h and 63a, 53h.

The operation of this form of device is substantially the same as described above, except that the changes in the 'tangential component of thrust tending to cause snap rotation of the control member are effected by variations in ilcgxure of the Bourdon tubes in response to changes in fluid pressure. Referring particularly to Bourdon tube 52o. when the iiuid pressure is such as to produce a tangential thrust in the direction indicated at 'Iii of such magnitude as to produce, in combination with the inwardly directed force due to the resilient compression of the tube, a resultant force R, this tube will tend to cause rotation of shaft 5| in a clockwise dicombined moment produced by the three Bourdon tubes is in that direction the control member 6I is rotated into, and held in, engagement with stop members 63a and 83h, thus opening the electrical. circuit. When the combined moment is in the reverse or counterclockwise direction, the bar 6| is rotated by snap action into engagement with stop members 62a and B2b, thus closing electric circuit between connecting leads 61 and 68, through contacts 62a and 64a, conductor strip 65, and contacts 64b and 62h.

For the same connection with'Fig. '1, rotative adjustment of ring 5B with respect to supporting plate 51 serves 64a and 64b electrically connectediixed position reasons as described above in to change the direction of the inwardly directed component of force exerted by the pressure responsive thrust members, and thus to adjust the device for operation at different values of fluid pressure.

In Fig. 10 I have shown a form of snap acting control device adapted for operation in response to mechanical displacement iof an actuating member M, such mechanical displacement being effected either by manual operation or by suitable mechanical means in remote response to a change of some condition being controlled.

In this case the shaft 1| is rotatably engaged and supported by three angularly spaced resilient thrust members formed as radially extending leaf springs 12a, 12b and 12e. Each of said springs is secured at its outer end to an annular supporting member 13, which may form part of a case for housing the mechanism, and is provided at its inner end with a knife edge tip engaging a V-shaped groove 1l in shaft 1|.

Control member 15, formed as an insulating bar, is "operatively connected to shaft 1| for rotation therewith, as in either Figs. 3 to 5 or Fig. 8, and stop members 16a, 1Gb and 11a, 11b are secured to an annular plate 18 of molded plastic material'or other suitable insulating material, in position to engage the ends of said control member and limit rotation thereof in counter-clockwise and clockwise directions respectively. -Insulating plate 18 is shown secured by rivets 19 to lugs 8| on supporting member 13. Either or both of the sets of stop members may be employed as contact members, but in this case I have shown only members 11a and 11b as electrical contacts, to which terminal wires 82 and 83 are connected, bar15 being provided with coasting contact members 84a and 84D electrically connected by a conductor strip 85.

The leaf springs 12a, 12b and 12o are shown as bowed longitudinally so as tobe resiliently compressibie, and are assembled in position under considerable radial compression, whereby each of said springs exerts an inwardly directed force against shaft 1| due to such compression. Each of said springs is also normally biased in a direction to exert against said shaft a tangential component of force in a direction tending to procontacts 84a and 84h are normally held in engagement with contacts 11a and 11b, to close the electric circuit.

The actuating member M. is shown as comprising a pin slidably mounted in a bearing member 81 secured to supporting member 13. The outer end of said pin projects through said bearing member to a position outside the casing, wherebyits outer end may be pressed inward manually or by any suitable operating mechanism which may in turn be controlled in response to some condition such as temperature, pressure er humidity. Said pin engages one of the resilient thrust members, such as 12a, at its inner end, and is normally held thereby in an outwardly displaced position and is provided with a shoulder 88 adapted to engage the inner member 81 to limit its outward movement. ward movement of actuating member M exerts a thrust against leaf spring 12a, causing the inner end of said spring yto exert against shaft 1| a produces a resultant indicated at R, and the arrangement is auch that under these` conditions the moment of the resultant force R tending to cause counter-clockwise rotation. exceeds the combined opposing moment of the forces exerted byleai springs 12b and 12o. Shaft 1i and control mem- .,er 1B are therefore rotated in a counter-clockwise direction, into engagement with stop members 16a and lib, thus opening the electric circuit.

It will be obviousthat, ii' the device is to operate as a normally o'pen switch instead o! being normally closed, stop members "a and 1Gb may be formed as contact members and connected to the lead wires B2 and 83, instead of stop members 'lla and 11b.

The actuating member M may be positioned so as to engage the resilient thrust member 12a at any desired distance from the inner end of member 12a, thus determining the sensitivity of the device from the standpoint of the amount of travel of said actuating member required to cause snap action oi the shaft and control member from one position to the other.

it will be evident that the devices described herein are inherently resistant to effects of vibration. Any vibratory movement tending to increase the tangential component of of the thrust members will cause a compensatJ` ing decrease in truust ofthe other members so that the combined forces tending to cause rotation of the central shaft remain substantially unaffected. Furthermore, the rotatably mounted means including the central shaft and the control member-1li, Si cr l5) mounted thereon at substantially the mid-length of said member, are substantially rotationally balanced so as to be substantially unaffected by -such vibrations. The weight of the control member ii, Si or 15 and of the Contact members carried thereby is equally distributed at opposite sides of the axis of rotation. The center or" gravity of the conductor strip 55 or 85 is also relatively closely adjacent the axis of rotation, and its weight may be made so small that any tendency thereof to cause rotation due to vibration is negligible.

The modified iorm of rotatably mounted controlmeans shown in Figs. l1 through 13 may be substituted for the control bar and contact means shown in any of the above described snapcontrol switch constructions, and is of particular advantage due to its being especially Well adapted to provide perfect rotational balancing about the axis or" the central shaft. Referring to these iigthrust of one` ures, the rotatably mounted control means com I prises an elongated metal conductor member 89 extending diametrically with respect to the axis or" rotation of shaft 90. The central portion of member 89 is secured to a metal strip Si and is insulated therefrom by one or more layersof insulating material indicated at 92. This insulating covering may advantageously be formed of glass fabric coated or impregnated with a resin or plastic of high insulating quality and good thermal stability, such as a silicone resin or varnish.

Metal strip 9i is shown g tabs 93 that are bent over to clamp the member 89 and insulation 92 securely in position, and is preferably connected to shaft 90 so as to permit pivotal or rocking movement oi' the control means about an axis perpendicular to the axis of the shaft, in the same manner and for the same purpose as describedv above in connection with strip 23 in Figs. 1 to 6.A

The conductor member 88 is formed at its ends provided with project- -ing to members I2a and IIb to receive suitably disposed contact members. In this case I have shown a contact arrangement adapted for use as a double-throw switch, comprising contact members 94a and Nb correspondabove and additional set of contact members 95a and 95h disposed at the opposite sides of the respective ends of member 8S. Fixed contact members 96a and lib correspond to contacts Ila and IIb above and may be mounted in a similar manner and connected to lead wires in one electric circuit. An additional set of fixed contacts 91a and 91h are mounted in positions corresponding to stop members i 1a and I 1b and may also be mounted in similar manner and connected to lead wires in another electric circuit.

In the position shown, contact members 94a and Sib are in engagement with contacts 96a and 96h. Snap action rotation in a clockwise direction breaks the connection in this circuit and brings contacts 95a and 95h into engagement with contacts 91a and 91h, closing the other circuit. Thus, contacts 96a, 96h and 91a, 91h act as stop members for limiting rotation oi shaft and the control means carried thereby in1 counter-clockwise and clockwise directions, respectively.l

Although the above described devices are shown adapted for operating electric switch means, they may also be adapted to operate other flow controlling means such as valves. By way of example, a temperature-responsive control device similar to that shown in Figs. 1 to 8 but adapted to voperate a valve for controlling the flow of iluid is illustrated in Figs. 14 and l5.

The central shaft IUI is resiliently supported by three resilient bimetallic thrust members |0211, iDZb and i 02o, the relationship, configuration and function of these members being similar to the members l, 2a, 2b and 2c above, and said members being mounted within a casing 103 formed integrally with or secured to a valve casing H14 provided with fluid inlet and outlet connections |05 and H15. The valve casing is also provided with an inwardly extending flange |01 defining a centrally located port I 08 and having a knifeedge valve seat IUS.

A control bar Ill is secured to shaft lili by a rivet H2. At one end of said bar is mounted a valve member i i3 carrying a disc III adapted' to be moved by said bar, upon rotation of shaft 10i, into and out of engagement with seat H19. A counter-weight H5 is preferably mounted on the other end of bar lll, at the opposite side of the axis of rotation ofthe shaft, the weight of member H5 being such that the entire rotatably mounted control means comprising shaft i D I, bar I i I, and the parts carried thereby is substantially rotationally balanced about said axis.

Valve seat IDS serves as a stop member limiting rotation of shaft I0! in a clockwisedirection in Fig. 14. A perforated plate or spider H6 is secured within the valve casing, and carries a stop member i l1 positioned for engagement with valve member l il to limit rotation of shaft I0! in the opposite direction. Member H1 is shown as a screw-engaging an internally threaded sleeve H8 on plate H8, whereby it may be adjusted to vary the amplitude oi the snap action movement of the valve between its closed and open positions.

The resilient bimetallic thrust members (02a, |02b and i02c are preferably mounted for rotative-adjustment relative to the stop members defining the limits of rotation of the shaft, in order to provide for adjusting the device to operate at different temperatures in the same manner as cured to inwardly projecting lugs l2| on a ring |22 rotatably mounted in a cylindrical portion |23 of casing |03. vSaid ring may be provided with an adjusting arm |24 projecting through a slot |25 in the cylindrical casing portion |23. whereby said ring may be rotated to bring the thrust members |02a, ||i2b and ||l2c to the desired position of adjustment. The parts may then be held in this position in any desired manner, as by bending arm |24 into tight engagement with the casing, or by soldering or otherwise securing said arm to the casing. Casing |03 is shown as provided with a suitable cover plate |26 removably secured thereto, and adapted to besecured to said casing after the above described mechanism is placed therein.

The operation of this form of device will be readily apparent in view of the foregoing description of the device shown in Figs. 1 to 6. The bimetallic thrust member may be so disposed as to cause snap action rotation of shaft IUI in a clockwise direction, moving the valve to closed position, when the temperature increases to a predetermined value. When the temperature decreases sufficiently to cause snap action rotation of said shaft in the opposite di rection, as described above in connection with Fig. 8, the valve is moved to open position, in engagement with stop member H1, permitting flow of fluid through port |08. The temperature limits at which the snap action movement of the valve occurs are determined by the position of rotative adjustment oi' the outer ends of the thrust members.

While I have described certain specific devices embodying the novel features and principles of snap acting control devices according to my invention, it is to be understood that the-invention includes various obvious modifications embodying the same essential principles. For example, in the temperature-responsive device of the type shown in Figs. 1 through 6, the binietallic members 2a, 2b and 2c may be made with only one loop extending each side of the radial center line instead of having two loops at each sida-as shown. If desired, the number of such loops could also be increased. Furthermore, the looped bimetal lic thrust members could be replaced, although somewhat less effectively, by resilient bimetallic members of spiral form having their inner con volutions mounted at angularly spaced positions about the axis of the central shaft and engaging the central shaft at the end of their outer convolutions. The foregoing description serves to illustrate the principles and applications of my invention and is not to be taken as limiting the scope thereof, which is defined in the appended claims.

I claim:

l. In a snap acting control device, the combination which comprises: a shaft; means resiliently supporting saidshaft for rotation about a longitudinal axis, comprising at least three resil ient members .disposed at different angular positions about said shaft and spaced less than 180 apart and each exerting against said shaft a thrust having an inward component toward said axis, at least one of said resilient members being operable to exert against said shaft a thrust having a tangential component and to selectively cause rotation of said shaft in opposite directions by snap action; and stop means for limiting rotative movement of said shaftin each direction.

2. In a snap acting control device, the combination which comprises: a shaft; means resiliently supporting said shaft for rotation about a longitudinal axis, comprising three resilient members disposed at different angular positions about said shaft and spaced less than apart and each exerting against said shaft a thrust having an inward component toward`said axis, at least one of said resilient members being operable to exert against said shaft a thrust having a tangential component and to selectively cause rotation of said shaft in opposite directions by snap action; and stop means for limiting rotative movement of said shaft in each direction; said resilient members being angularly adjustable with respect to said stop means.

3. In 'a snap acting control device, the combination which comprises: a shaft; means resiliently supporting said shaft for rotation about a longitudinal axis, comprising three resilient members disposed at different angular positions about said shaft and spaced less than 180 apart and eachexerting against said shaft a thrust having an inward component toward said axis, at least one of said resilient members being operable 'to exert against said shaft a thrust having a tangential component and to selectively cause rotation of said shaft in opposite directions by snap action;a control member connected to said shaft and operable in opposite directions upon opposite rotational movement of said shaft; and means for limiting movement of said control member in each direction.

4. In a snap acting control device, the combination which comprises: a shaft; means resiliently supporting said shaft for rotation about a\ longitudinal axis, comprising bers disposed at differentv angular positions about said shaft and spaced less than 180' apart and each exerting against said shaft a thrust having an inward component toward said axis, at least one of said resilient members being operable to exert against said shaft a thrust having va tangential component and to selectively cause rotation of said shaft in opposite directions by snap action; a control member connected to said shaft for rotation therewith about said axis and substantially rotationally balanced about said axis; and means for limiting rotative movement of said control member in each direction.

5. in a snap acting electric switch device, the combination which comprises: a shaft; means resiliently supporting said shaft for rotation about a longitudinal axis, comprising three resilient members disposed at different angular positions about said shaft and spaced less than 180 apart andeach exerting against said shaft a thrust having an inward component toward said axis, at least one of said resilient members being operable to exert against said shaft a thrust having a tangential component and to selectively cause rotation of said shaft in opposite directions by snap action; a control member connected to said shaft for rotation therewith about said axis and provided with electrical contact means; contact means positioned to engage the contact means on the control member upon rotation thereof in one direction and limiting rotation in that direction; and stop means for limiting rotation of said control member in the opposite direction.

three resilient mem- A 6. .In a snap acting electric switch device, the combination which comprises: a shaft; means resiliently supporting said shaft for rotation about a longitudinal axis, comprising three resilient members disposed at different angular positions about said shaft and spaced less than 180 apart and each exerting against said shaft a thrust having an inward component toward said axis, at least one of said resilient members being operable to exert against said shaft a thrust having a tangential component and to selectively cause rotation of said shaft in opposite directions lby snap action; a control member extending transversely with respect to said axis and connected to said shaft for rotation therewith about said axis, said control member being pivotally mounted on said shaft for movement about an axis extending transversely with respect to the shaft; two contact members rriounted on the respective ends of said control member; two coacting contact members positioned for engagement by the respective contact members on the control member upon rotation of said shaft and control member in one direction about said first-mentioned axis and limiting rotation thereof in that direction; and stop means for limiting rotation oi' said shaft and control member in the opposite direction.

7. in a snap acting device for controlling fluid flow, the combination which comprises: a shaft; means resiliently supporting said shaft for rotation about a longitudinal axis, comprising three resilient members disposed at different angular I positions about said shaft and spacedlless than 180 apart and each exerting against said shaft a thrust having an inward component toward said axis, at least one of said resilient members being operable to exert against said shaft a thrust having a tangential component and to selectively cause rotation of said shaft in opposite directions by snap action; a control member oonnected to said shaft for rotation therewith about said axis; a valve member mounted on said control member; a valve seat positioned for engagement by said valve member upon rotation of said control member in one direction and limiting rotation thereof in that direction; and stop means for limiting rotation of said control member in the opposite direction.

8. fn a snap acting control device, the cornbination which comprises: a shaft; three resilient members disposed at different angular positions about said shaft, spaced less than 130 apart, and engaging said shaft at their inner ends to resiliently support the shaft for rotative movement about a iongitudinal axis; each of said resilient members exerting against said shaft a thrust having an inward component toward said axis and at ieast one of said resilient members being responsive to a variable `condition to exert against said shaft a tangential component of thrust directed selectively in opposite directions about said axis upon changes in said condition and thereby cause rotation of said shaft in opposite directions by snap action; a control member operatively connected to said shaft for movement in opposite directions upon opposite rotative movements of said shaft; and means for limassen? ment about a longitudinal axis; each of said resilient members exerting against said shaft a thrust having an inward component toward said axis Vand being responsive to a condition to be consaid shaft; and means for limiting movement of iting movement of said control member in each direction.

9. In a snap acting control device, the combination which comprises: a shaft; three resilient members disposed at different angular positions about said shaft, spaced less than 180 apart, and engaging said shaft at their inner ends to resiliently support the shaft for rotative movesaid control member in each direction.

10. In a snap acting control device, the combination which comprises: a shaft; three resilient members disposed at different angular positions about said shaft, spaced less than 180 apart, and engaging said shaft at their inner ends to resiliently support the shaft for rotative movement about a longitudinal axis; each of said resilient members exerting against said shaft a thrust having an inward component toward said axis and being responsive to a condition to be controlled, to exert against said shaft a tangential component of thrust directed selectively in opposite directions about said axis upon changes in said condition; a control member operatively connected to said shaft for movement in opposite directions upon opposite rotative movements of said shaft: and stop means for limiting movement of said control member in each direction; said resilient members being angularly adjustable with respect to said stopmeans.

l1. In a snap acting control device, the combination which comprises: a shaft; three resllient members disposed at different angular positions about said shaft, spaced less than 180 apart, and engaging said shaft at their inner ends to resiliently support the shaft for rotative movement about a longitudinal axis; each of said resilient members exerting against said shaft a thrust having an inward component toward said axis and being responsive to a condition to be controlled, to exert against said shaft a tangential component oi thrust directed selectively in opposite directions about said axis upon changes in said condition; a control member connected to said shaft for rotation therewith about said axis and substantially rotationallv balanced about said axis; and means for limiting rotative movement of said control member in each direction.

l2. In a snap acting electric switch device, the combination which comprises: a shaft; three resilient members disposed at different angular positions about said shaft, spaced less than apart, and engaging said shaft at their inner ends to resiliently support the shaft for rotative movement about a longitudinal axis; each of said resiient members exerting against said shaft a thrust having an inward component towardsaid axis and being responsive to a condition to be controlled, to exert against said shaft a tangential component of thrust directed selectively in opposite directions about said axis upon changes in said condition; a control member connected to said shaft for rotation therewith about said axis and provided with electrical contact means; contact means positioned to engage the contact means on the control member upon rotation thereof in one direction and limiting rotation in that direction; and stop means for limiting rotation of said control member in the opposite direction.

13. In a snap acting electric switch device, the combination which comprises: a shaft; three reends to resiliently l siiient members disposed at different angular poaxis and being responsive to a condition to becontrolled, to exert against said shaft a tangential component of thrust directed selectively in opposite directions about said axis upon changes in said condition; a control member extending transversely with respect to said axis and connected to said shaft for rotation therewith about said axis. said control member being pivotally mounted on said shaft for movement about an axis extending transversely with respect to the shaft; two contact members mounted on the respective ends of said control member; two coacting contact members positioned for engagement by the respective contact members on the control member upon rotation of said shaft and control member in one direction about said firstmentioned axis and limiting rotation thereof in that direction; and stop means for limiting rotation of said shaft and control member in the opposite direction.

shaft. spaced less than 180 apart, and said shaft at their inner ends to resiiiently support the shaft for rotative movement about a longitudinal axis; each of said resilient bimetallic i4. In a snap acting device for controlling duid l now, the combination which comprises: a shaft; three resilient members disposed at different anguiar podtions about said shaft, spaced le'ss than 180' apart, and engaging said shaft at their inner endsl to resiliently support the shaft for rotative movement about a longitudinal axis; each of said resilient members exerting against said -shaft a thrust having an inward component toward said axis and being responsive to a condition to be controiied.to exertagainst said shaftatangentiai component of thrust directed selectively in opposite directions about said axis upon chantes in saidcondition; a control member connected to said shaft for rotationtherewith about said axis; a valve member mounted on said control member;

a valve seat positioned for engagement 'by saidv valve member upon rotation of said control member in one direction and limiting rotation thereof in that direction; and stop means for limiting rotation of said control member'inthe opposite dirootkli. A

i5. In a temperature responsive snap acting members exerting against said shaft a thrust having an inward component toward said axis and being responsive to temperature, to exert said shaft a tangentialcomponent of thrust directed selectively in opposite directions about said axis upon changes in temperature; a control member operatively connected to said shaft for movement in opposite directions upon opposite rotative 'movements of said shaft; and-means for limiting movement of said control member in each direction.

16. In a pressure responsive snap acting' control device, the combination which comprises: a shaft; three resilient pressure responsive members disposed at different angular positions` about said shaft spaced less than 180 apart, and engazing said shaft at their inner ends to reslliently support' the shaft for rotative movement about a longitudinal axis; each of said resilient members exerting against said shaft a thrust having an inward component toward said axis and being responsive to'pressure to exert against said shaft a tangential component of thrust directed selectively in opposite directions about said axis upon changes in pressure; a control member operatively connected tosaid shaft for movement in opposite directions upon opposite rotative movement of said shaft; and means for limiting movement of said control member in each direction.

17. In a snap acting control device, the combination which comprises; a shaft; three resilient members disposed at different angular positions about said shaft. spaced less than 180 apart. and engagingsaidshaftat theirinnerendstore siliently support the shaft for. rotative movemmt about a longitudinal axis; each of said resilient members exerting against said shafta thrust hav ing an inward component toward said axis and also having a tangential component rotatively biasing said shaft in one direction; a movably mounted actuating member adapted to engage anddisplaceoneofsaidresilientmembersto causesaidonsmembertoexertagdnstsaidshaft e a tangential component in the opposite direction control device. the which comprises:

ashaft;threeresilienthimetailicmembersdis posedatdifferentangularpositionsaboutsaid tocauserotationdsaidshaftinsaidopposite directiomandmeansforiimitlngrotationofsaid shaftinnchdirection.

JAmRCAllPBEI-L. 

